Doppler-Shifted Cyclotron Resonance of Helicon Waves in Single-Crystal Aluminum

Abstract

Results are presented of measurements of Doppler-shifted cyclotron resonance (DSCR) of helicon waves in single-crystal aluminum with the magnetic field and helicon propagation along the [100] and [110] directions. The Gaussian radius of curvature of the Fermi surface in the second zone is measured at the point where the surface normal is along [100]. The experimental value for the radius of curvature is 0.99±0.03 times the free-electron value, in agreement with the expected value. For [110], it is shown that DSCR absorption edges at an elliptic limiting point on an arm of the third-zone Fermi-surface "monster," and on finite orbits involving a large fraction of the electrons on the second-zone surface, are expected to occur almost simultaneously. The difficulties associated with interpretation of the data when finite-orbit absorption edges exist are discussed. It is shown that beyond an estimate of the [110] curvature, which is in surprisingly good agreement with the calculated value, a more precise interpretation of the [110] data cannot be justified. The merits of the helicon DSCR method for Fermi-surface studies are discussed, and it is concluded that in general useful information can be obtained only on very pure samples with ${\omega }_c\tau \gtrsim 100$, where ${\omega }_c$ is the cyclotron frequency and $\tau$ the conduction-electron relaxation time.